RESUMO
This study aimed to evaluate the effects of oral administration of calcium (Ca) formate in the postpartum of high-producing dairy cows on calcemia, on other blood biochemical markers, and on the occurrence of diseases at the beginning of lactation. One hundred and twenty healthy Holstein cows, distributed according to the lactation order (first, second, third and fourth to sixth), were treated or not with oral Ca formate (two doses: one after calving and one 24 h later; equivalent to 50 g of Ca per dose), comprising 8 groups (n = 15). The following variables were measured in the blood serum of samples collected after calving (0 h) and after 24, 48, 72, and 96 h: total Ca, phosphate (P), magnesium (Mg), non-esterified fatty acids (NEFA), beta-hydroxybutyrate (BHB), glucose, total protein (TP), albumin (Alb), urea nitrogen (BUN), aspartate aminotransferase (AST) and gamma-glutamyl transferase (GGT). Blood BHB was also measured at 7, 14, and 21 DIM. For the assessment of disease occurrence, cows were distributed in treated (n = 60) and untreated (n = 60) groups and in hypocalcemic (n = 71) and normocalcemic (n = 49) groups. Two-way repeated measures ANOVA and a chi-square test were used for comparisons. The lactation order did not influence the studied blood constituents, except for primiparous cows which had the highest calcemia. Serum Ca was lower up to 24 h and increased after 48 h and subclinical hypocalcemia (SCH) ([Ca] < 2.125 mmol/L) was more frequent in cows with a higher number of lactations. Treatment with Ca formate had no effect on the variation of serum Ca and the other studied variables in the first days of lactation. Treated and untreated cows did not differ in terms of milk yield at 21 DIM, the presentation of diseases at the beginning of lactation, the rate of discard or death up to 60 DIM and the frequency of SCH (60 % and 58 %, respectively). Hypocalcemic cows became more ill (64.8 % vs. 42.9 %; P = 0.028) and had a higher frequency of retained placenta (43 % vs. 20.7 %; P < 0.001). Oral administration of Ca formate after calving and 24 h later is not justified as a preventive measure to be adopted indiscriminately in dairy herds. Studies involving larger number of animals may clarify whether the selective treatment of cows with a higher risk of hypocalcemia is advantageous.
